A current of several tens of A to several hundreds of A flows through a semiconductor transistor for use in a power converter or the like, which causes large heat generation and leads to a temperature rise of the semiconductor transistor. The temperature rise of the semiconductor transistor is suppressed by a cooling device. In some cases, however, a temperature rise of the semiconductor transistor cannot be suppressed sufficiently.
For example, in a short-circuit failure that might happen in a power converter circuit or the like, a current flowing through a semiconductor transistor increases abruptly, which causes an over-current. When an over-current occurs in a semiconductor transistor due to, for example, a short-circuit, heat generation is caused abruptly, whereby the temperature of the semiconductor transistor rises abruptly. In an over-temperature state as a result of an abrupt temperature rise, the semiconductor transistor cannot be controlled and are broken down in some cases. In such cases, the power converter circuit may be severely affected at times.
In order to prevent a breakdown of a semiconductor transistor due to an abrupt temperature rise, it is required to rapidly and accurately sense a temperature of a semiconductor transistor or a current flowing through the semiconductor transistor and control the semiconductor transistor, to thereby protect the semiconductor transistor from an over-temperature state.
For example, Patent Document 1 (page 10, FIG. 3) and Patent Document 2 (pages 5 and 6, FIG. 1) disclose semiconductor devices each containing an element for sensing a temperature (hereinafter, also referred to as a “temperature sensing element” in some cases) as a semiconductor device of the conventional art that can sense the temperature of a semiconductor transistor (hereinafter, merely referred to as a “transistor” at times).
In the semiconductor devices disclosed in Patent Documents 1 and 2, a diode, resistor, or the like is provided as a temperature sensing element on a transistor or in the vicinity thereof, and the temperature of the transistor is sensed from the temperature dependence in characteristics of the temperature sensing element. For example, in the semiconductor device disclosed in Patent Document 2, the temperature of the transistor is sensed from the temperature dependence of a PN diode being a temperature sensing element that is formed on a substrate of a wide bandgap semiconductor such as a silicon carbide.
As a semiconductor device of the conventional art that can sense the current flowing through a semiconductor transistor, for example, Non-Patent Document 1 (page 768, FIG. 6) and Patent Document 3 (page 4, FIG. 1) disclose semiconductor devices each containing an element for sensing a current (hereinafter, referred to as a “current sensing element” at times).
In the semiconductor devices disclosed in Non-Patent Document 1 and Patent Document 3, a part of a plurality of cells constituting a transistor is used as a current sensing element. For example, in the semiconductor device described in Patent Document 3, a part of a plurality of cells constituting a semiconductor transistor is provided, as a current sensing cell, in the vicinities of the center and outer periphery of a semiconductor chip, and the current flowing through the semiconductor chip is sensed based on an average value of the sense currents sensed by the current sensing cell.
In the semiconductor devices disclosed in Non-Patent Document 1 and Patent Document 3, a transistor includes a group of partial cells (hereinafter, referred to as a “sense cell group”) that is used as a current sensing element and a group of cells (hereinafter, referred to as a “main cell group”) that carriers most of the current conducted to the transistor. The technologies disclosed in Non-Patent Document 1 and Patent Document 3 are adopted as the technology of sensing the current flowing through the transistor also in, for example, the semiconductor device disclosed in Patent Document 1 above.